1. Field of the Invention
The invention involves a method and a device for controlling the data traffic in an ATM network, wherein a number of nodes are connected via a closed loop, and wherein each node may be equipped with a number of access ports for the sending and receiving of ATM cells.
2. Description of the Background Art
In a network that operates based upon packet-oriented data transmission among several nodes, traffic management is of central importance. In an ATM system (ATM=asynchronous transfer mode) having a loop-type structure, this need for control of data traffic generally results in the sum of all the band widths of all the system connections (access ports) being greater than the band width of the closed loop.
One example of this is an ATM network, known in the art from U.S. Pat. No. 5,475,682, in which the ATM cells that are received in one node are distributed, based upon their destination, to various output queues, from which they are then transmitted. The nodes can signal an overload situation to the nodes up the line using so-called back-pressure signals. In the nodes up the line, the data packets intended for the signaling nodes are then temporarily stored in a buffer. If the buffer is full, the data packets are transmitted to the nodes down the line anyway. There, in an overload situation, packets having the longest burst are shifted out of memory and are lost. The object of the method in the invention is to prevent one node from blocking all preceding nodes.
Because the data are generally received irregularly, it may be important to determine and to monitor statistically the size of the bursts. To implement this monitoring function, various leaky-bucket systems are known in the art (comp. for example U.S. Pat. Nos. 5,448,567; 5,295,135; 5,339,332, and 5,418,777.
As is known, one important advantage of ATM systems is that the widest variety of services can be provided via one and the same network. So the key is to design the traffic management system such that the various specifications (maximum permissible delay, cell loss rate, band width, etc.) will also be met or fulfilled. It is particularly important to prevent one service of lower priority from interfering with, or even blocking, one of higher priority.